1. Field of the Invention
This invention relates in general to laser induced detecting and ranging (LIDAR) systems.
2. Background of the Invention
Current methods for bio-warfare agent (BWA) sensing rely on point detectors, where a local sample is taken—either in the form of air sampler or a swab—and analyzed. The analysis can be based on immuno-assay, culture, or even a fluorescence based aerosol particle sizer or detector. A stand-off detector does not need to bring the sample to it for analysis, and is thus able to provide advance warning even before the BW agent arrives near the sensor, and operates continuously—not batch processing.
Stand-off sensors for the detection and discrimination of bio-warfare agent aerosols have been used for performing the task of round-the-clock surveillance to provide advance warning for personnel of the release of a BWA. A fluorescence lidar, which first detects aerosol particles by elastic light scattering and then employs UV laser excitation to generate auto-fluorescence from the proteins contained in the BWA particles for discrimination, is well established as a technique of choice for the stand-off BWA sensor. Although fluorescence sensors are not capable of specific identification, their real-time capability for standoff and point detection and discrimination with low false alarm rates makes them well suited as the first sensor in a suite of sensors.
However, such UV fluorescence lidars have conventionally required a large, high energy UV laser source and are consequently bulky, and expensive, which in turn have limited the utility of standoff lidar sensors. Indeed, in view of the small fluorescence cross sections for most of the BW agents, fluorescence lidars have relied upon high peak power (multi kW) pulsed solid state UV lasers to generate sufficient fluorescence signal from BW agent aerosols to achieve adequate measurement range and sensitivity.
Thus, the size, cost, and limited utility of UV laser sources have limited the application of UV laser sources in lidar sensor applications.